Method for separating immiscible fluids of different specific gravities

ABSTRACT

A tubular centrifugal separator for immiscible fluids of different specific gravities comprises a tubular body provided with at least one concentric internal partition and fed at one end with the mixture of fluids to be separated. Included are also, at least two separate means for driving the fluid in rotation, the second of which is placed downstream from the end of an internal partition inside the tubular body. Extraction ducts are provided to withdraw the separated fluids and means to feed back remaining fractions of the mixture.

This is a continuation of application Ser. No. 429,576 filed Sept. 30,1982, now U.S. Pat. No. 4,478,712.

BACKGROUND OF THE INVENTION

The present invention concerns a device for separating immiscible fluidsof different specific gravities.

Centrifugal separators are known which are capable of subjecting astream formed of a mixture of immiscible fluids of different specificgravities to the action of centrifugal forces. The fluid of low specificgravity is essentially collected in the central portion of the finalstream, whereas the fluid of higher specific gravity is driven off atthe periphery. An annular partition makes it possible to physicallyseparate the two fluids. Such separators are described in the GermanPat. No. 1,186,412 the U.S. Pat. No. 3,746,173 and the Swiss Pat. No.536,126.

In practice, it is not possible to define the precise boundary or limitbetween the fluids of the final stream, this limit varies, moreover,according to modifications in the relative amounts of the fluids at theinlet of the separator.

However, for certain applications, it is necessary to achieve a completeseparation of the fluids so that each of the obtained streams containsonly a single fluid.

In the centrifugal separators of the above-indicated type, it ispossible to isolate from the final stream, by suitably selecting thediameter of the annular partition, a stream composed of a determinedfraction of one single fluid. But the remaining portion of the finalstream is constituted of a mixture of fluids which might be treated in asecond, serially connected, centrifugal separator. Thus, betterseparating performances are obtained but, on the other hand, theseparation of the fluids is not complete. It is possible, of course, toincrease the number of separators, but there is a physical limit formingan obstacle thereto which results from the size to be given to theannular separating partition and moreover, one of the obtained fluids isnot completely pure.

In certain separators, the intermediate portion of the stream, locatedbetween the central stream and the peripheral stream, is reintroduced atthe inlet of the separator. Such separators are described in the articleof M. BOHNET entitled "Trennen nicht mischbarer Flussigkeiten" publishedin "Chemie Ingenieur Technik", vol. 48 No. 3 pages 177-264, and inFrench Pat. No. 2,130,579.

SUMMARY OF THE INVENTION

It is in order to improve the quality of the fluids separation that thepresent invention provides a device operating on the principle of thecentrifugal separation of immiscible fluids of different specificgravities, said device not being subject to the aboveindicateddisadvantages and making possible a substantially complete separation ofthe fluids forming the mixture.

Finally, according to an alternative embodiment of the presentinvention, the device is adapted for treating fluid mixtures whoseproportions of different components vary to a large extent.

The device according to the invention comprises a tubular body, providedwith at least one internal coaxial partition, wherein the mixture isintroduced at a first of its ends and discharged, at least partly, atits second end. First means is provided adapted to impart to saidmixture, when circulating through said body, a motion having arotational component about the axis of the tubular body and means forfeeding back the stream flowing out from said second end. The devicefurther comprises at least second means adapted to impart to the fluidpassing therethrough a rotational component about the axis of thetubular body, said second means being placed from the end of one of thepartitions located inside said tubular body.

According to an alternative embodiment of the device of the invention,at least one of the concentric partitions extends partly outside themain section of the tubular body, thereby forming a tubular extensionthereof whose end forms the second end of said body, and said secondmeans are placed inside said partition in said tubular extension.

According to a first embodiment of the device of the invention, thetubular body comprises first mixture extraction means communicating withthe annular space formed between the external wall of the tubular bodyand the adjacent coaxial partition, and second extraction meanscommunicating with the space defined by a central coaxial partition ofthe tubular body. It is the partition adjacent to the external wall ofthe tubular body which forms a tubular extension of the latter.Downstream from the second means for driving the fluid in rotation isprovided third extraction means communicating with the annular spacecomprised between the tubular extension and a coaxial adjacent internalpartition, and fourth extraction means communicating with the spacedefined by a coaxial central partition.

The annular space comprised between said central partition and saidpartition adjacent to the tubular extension communicates with saidfeedback means.

According to a second embodiment of the device of the invention, thetubular body comprises first extraction means communicating with theannular space comprised between the external wall of the tubular bodyand the adjacent coaxial partition. It is the latter partition whichforms the tubular extension of the tubular body. Downstream from saidsecond means for driving the fluid in rotation is provided secondextraction means communicating with the space defined by the coaxialcentral partition. The annular space comprised between said centralpartition and said tubular extension communicates with said feedbackmeans.

A third embodiment of the device of the invention comprises, between thepartition placed downstream said first means for driving in rotation thefluid mixture and said second means for driving in rotation the fluidmixture, at least one assembly of intermediary means imparting to thefluid mixture a motion having a rotational component about the axis ofthe device and an annular partition defining a space wherethroughcirculates a fraction of one of the components having traversed saidauxiliary rotary driving means, this space communicating with a fluidextraction duct.

According to an embodiment particularly useful when the proportions ofthe different fluids to be separated vary to a large extent, the deviceof the invention comprises for each of the fluids of the mixture, adischarge line communicating with the corresponding extraction meansformed by a duct. At least one of the extraction ducts is equipped witha two-way valve and with a sensor supplying a signal characteristic ofthe nature of the stream circulating through the extraction duct, saidsensor being associated with means for placing the valve in a positionof communication between the extraction duct and the correspondingdischarge line when the flow circulating through the extraction ductconsists exclusively of one of the mixture components, as well as meansplacing the valve in a second position interrupting the communicationbetween the extraction ducts and the corresponding discharge line whenthe stream flowing through the extraction duct does not consistexclusively of a single one of the mixture components.

In its second position, the valve optionally establishes communicationbetween the extraction duct and said feedback means.

The feedback of the fluid mixture must be effected upstream of the meansfor driving the fluid in rotation, for example at the inlet of the firstend of the tubular body.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and all its advantages will bemade clearly apparent from the following description of examples ofembodiments of the device according to the invention, as describedhereinafter and illustrated by the accompanying drawings wherein:

FIG. 1 shows a first embodiment of the device according to theinvention,

FIG. 2 shows a second embodiment of the device,

FIG. 3 relates to modifications which may be brought to the device whenthe proportions of the fluids vary to a large extent,

FIG. 4 illustrates the use of the device in the case of the separationof three immiscible fluids of different specific gravities forming themixture,

FIG. 5 illustrates a third embodiment of the device, and

FIG. 6 shows one case of use of the device.

DETAILED DISCUSSION OF THE INVENTION

FIG. 1 diagrammatically shows a first embodiment of the device accordingto the invention.

The latter comprises a tubular body 1 into which is introduced, at oneof its ends 2, a mixture formed of two fluids F₁ and F₂ of differentspecific gravities d₁ and d₂, such that d₁ <d₂.

By immiscible fluids it is also meant a mixture formed of a fluidcontaining suspended solid particles or a diphasic fluid comprising aliquid phase and a gaseous phase.

Inside body 1 are placed first means 3 adapted to impart to the mixtureof fluids F₁ and F₂, a motion having a rotational component about theaxis of tube 1.

These means for driving in rotation the mixture are, for example, formedby a rotor carrying blades, having preferably a suitable profile, suchfor example as that described in the U.S. Pat. No. 3,517,821.

Downstream from these first means 3 for driving in rotation the fluid,are placed a first annular partition 6, coaxial to the tubular body 1,defining therewith a first annular space 7, and a second annularpartition 8, coaxial to the tubular body having a diameter smaller thanthat of the first partition 6.

The central space 9 of the tubular body defined by the second partition8 communicates with second extraction means 11.

The first partition 6 extends partly outside the main section of thetubular body so that it forms a tubular extension of the latter whoseend constitutes the second end of the tubular body.

Second means 14 for driving in rotation the fluid are placed inside thefirst partition 6 downstream the end of the second partition 8.Downstream from said second means 14 for driving the fluid in rotationare placed a third and a fourth annular partitions having the respectivereferences 16 and 18 in FIG. 1. These partitions are coaxial andinternal to the first partition 1. The third partition 16 defines withthe extension of the first partition 6 a third annular space 17 whichcommunicates with extraction means 20. The fourth partition 18 of asmaller diameter than that of the third partition 16, defines a centralspace of the tubular extension. This space is connected to fourth fluidextraction means 21.

The space 22 defined between the third and the fourth partitions,respectively referenced 16 and 18, communicates with fluid feedbackmeans 13. In the case of FIG. 1, the feedback is effected upstream thefirst means 3 for driving the fluid in rotation. Alternatively, it couldhave been effected upstream the second means 14 for driving the fluid inrotation.

In the case of FIG. 1, the second means 14 for driving the fluid inrotation are driven by the motor 4.

The operation of the device is indicated below.

The mixture of fluids F₁ and F₂ is introduced into body 1 at its end 2.The rotatory driving means 3, driven by the motor 4, imparts to themixture a motion having a rotational component about the axis of body 1.Under the action of the centrifugal force, the fluid F₁, of specificgravity d₁ is collected in the central portion of the stream while thefluid F₂ concentrates at the periphery.

The diameter of the first partition 6 is determined so that in the space7 circulates a fraction of fluid F₂ which is discharged through line 10.

The diameter of the second partition 7 is selected so that in space 9circulates only a fraction of fluid F₁ which is discharged through line11.

The remaining mixture of fluids F₁ and F₂ which circulates through theresidual annular space 12, is subjected to a second centrifugation bythe second means 14 for driving the fluid in rotation. Under the actionof the centrifugal force the fluid F₁ is gathered in the central portion19 of the stream and the fluid F₂ at the peripheral portion 17. Thestream circulating through space 22 is fed back upstream said firstmeans 3 for driving the fluid in rotation.

The diameter of the partitions 16 and 18 is so determined that throughthe spaces 17 and 19 circulates substantially a single type of fluid,respectively F₂ and F₁.

The diameters of the partitions 6, 8, 16 and 18 are determined asabove-indicated in relation with the proportion of fluids F₁ and F₂introduced into the device.

Preferably, but not exclusively, the diameters of the partitions 6, 8,16 and 18 are so selected as to provide for the extraction of the samerelative amounts of fluids F₁ and F₂. Thus, the mixture fed back throughline 13 contains substantially the same proportions of fluids F₁ and F₂as the fluid mixture to be treated.

The advantage of this embodiment, in addition to the quality of theseparation of the mixture components achieved therewith, consists of thefact that the second rotatory driving means 14 and the separatingpartitions associated therewith may be of small size, since they treat alimited flow of mixture of fluids F₁ and F₂. Moreover, the flow of fluidmixtures fed back at the inlet of the device is small.

FIG. 2 shows another embodiment of the device which can be used even toseparate fluids whose specific gravities are not very different. Thesame references have been used to designate the same elements.

This embodiment makes use of means 3 and 14 for driving the mixture inrotation. The first partition 6 is interposed between these means anddefines with the tubular body 1 a space 7 wherethrough circulates afraction of fluid F₂ which is discharged through line 10.

The remaining mixture, formed of the totality of fluid F₁ and of theremaining fraction of fluid F₂, is subjected to the action of the secondrotatory driving means 14. The second partition 8, interposed betweenthe means 14 and the end 5 of the tubular body 1, isolates the centralportion of the stream issuing from the second rotatory driving meanswherethrough circulates only a fraction of fluid F₁ which is dischargedthrough line 11.

The mixture of fluids F₁ and F₂ circulating through the residual space12 is fed back to the inlet of the device through line 13.

The preceding description shows that there is obtained, in theextraction lines, single-fluid streams, at least when the proportions offluids F₁ and F₂ are liable to be subjected to limited variations at theinlet of the device. The diameters of the separating partitions aredetermined in accordance with these variations so that at any time, thepartitions isolate stream portions containing only one single fluid.

In the case where the proportions of fluids F₁ and F₂ vary to a largeextent at the inlet of the device, for example, when the content offluid F₁ or F₂ varies between 0 and 100%, it is advisable to modify thedevice of the invention, according to the embodiments illustrated inFIG. 3.

A sensor 22 is placed on the fluid F₂ extraction line 10 to indicatewhether the fluid circulating through said line is exclusively composedof fluid F₂ or whether it is composed of a mixture of fluids F₂ and F₁.This sensor may be of any known type. For example, the sensor determinesthe presence of one and/or the other of the two fluids by measuring theelectric resistance of the stream flowing through line 10. This sensorcontrols a two-way valve 24 through a circuit diagrammatically shown at23.

When the sensor 22 delivers a signal indicating the presence of fluid F₂alone, the valve 24 is placed in its first position which connects line10 to a line 25 for discharging fluid F₂.

When the signal from sensor 22 indicates the presence of fluid F₁ inline 10, the control circuit 23 actuates the valve 24 which is placed inits second position where it stops the communication between theextraction line 10 and the fluid F₂ discharge line 25.

In its second position, the valve may simultaneously put line 10 incommunication with a line 26 opening upstream of at least one means fordriving the fluid in rotation. In the case of FIG. 3, line 26 opens atthe inlet of the device.

Similarly, a sensor 27 is placed at the outlet of the device on the line11 for extracting fluid F₁ and controls a two-way valve 29, through acircuit 28.

When the signal delivered by sensor 27 indicates that the stream throughline 11 is exclusively composed of fluid F₁, the valve 29 is placed intoa position at which line 11 is exclusively connected with line 30 fordischarging fluid F₁.

When the signal delivered by sensor 27 indicates the presence of fluidF₂ in line 11, the valve 29 is placed into its second position at whichthe line 11 is connected with a line 31 which opens upstream of at leastone member for driving in rotation the fluid. In the case of FIG. 3,line 31 opens at the inlet of the device.

Of course, the distance between each sensor and the valve controlledtherewith is selected sufficient to make effective the operation of thevalve before it is traversed by the fluid mixture, whereas, in the caseof detection of a single fluid, a temporization delays the operation ofthe valve.

The operation of the device is obvious from the preceding description.

Under normal operating conditions, only fluid F₂ flows through line 10.The valve 24 puts in communication lines 10 and 25. Similarly, onlyfluid F₁ flows through line 11 when it is put in communication with line30.

When, at the inlet of the device, the proportion of fluid F₂ decreasesbelow the proportion of the fluid extracted through line 10, some fluidF₁ flows through line 10. The sensor 22 detects the presence of saidfluid F₁ and the valve 24 puts in communication the lines 10 and 26. Thetotality of fluid F₂ is accordingly fed back to the device, therebyincreasing the proportion of fluid F₂ at the inlet of the device. Duringthis time, the fluid flowing through line 11 consists exclusively offluid F₁ which flows into line 30 through the valve 29.

When the proportion of fluid F₂ at the inlet of the device reaches avalue at which only fluid F₂ flows through line 10, the sensor 22actuates the valve 24 to put again in communication the lines 10 and 25.

Conversely, when the proportions of fluid F₁ at the inlet of the devicedecreases below a value at which the sensor 27 indicates the presence offluid F₂ in line 11, the valve 29 puts in communication the lines 11 and31, thereby providing for the feed back of the totality of fluid F₁ tothe inlet of the device, thus increasing the proportion of fluid F₁ atthe inlet of said device. During this time, the fluid flowing throughline 10, composed exclusively of fluid F₂, flows into line 25 throughthe valve 24.

When the proportion of fluid F₁ at the inlet of the device reaches avalue at which only this fluid flows through line 11, the sensor 27actuates the valve 29 to restore the communication between lines 11 and30.

The above description is based on the case of separation of twoimmiscible fluids of different specific gravities. The device may alsobe used to separate more than two fluids, as diagrammatically shown inFIG. 4, wherein it has been assumed that the initial mixture containedthree fluids F₁, F₂, F₃ of respective specific gravities d₁, d₂, d₃ suchthat:

    d.sub.1 <d.sub.2 <d.sub.3

Two serially interconnected devices A and B are used, the first device Adelivering a portion of fluid F₃ and, on the other hand, a mixture offluid F₁ and F₂ which are then separated by the second device B.

FIG. 5 shows another embodiment. According to the latter, the fluidentering the device is subjected to the action of first rotatory drivingmeans diagrammatically shown at 3 and an annular partition 6 separatesthe fraction of fluid F₂ which is discharged through line 10.

The mixture of fluid F₁ and of the remaining fraction of fluid F₂ isthen subjected to the action of new rotatory driving means 3a associatedwith an annular partition 6a which separates a new fraction of fluid F₂,discharged through line 10a. Other rotatory driving means 3b . . . 3n,serially connected and respectively associated with the annularpartitions 6b . . . 6n, permit extraction of the major portion of fluidF₂.

The remaining mixture is then subjected to the action of rotatorydriving means 14 associated with an annular partition 8 which isolates afraction of fluid F₁ discharged through line 11.

The remaining mixture is recycled through line 13.

Modifications may be brought to the various embodiments of the inventionillustrated by the different figures.

Thus, it is possible to provide means for regulating the rotation speedof the means for driving the mixture in rotation.

In the embodiments making use of several rotatory driving means, thesemeans may be driven by different motors, at different speeds, either byacting on these motors or by interposition of mechanical reducers.

The modifications illustrated in FIG. 3 may be brought to each of theother embodiments of the device according to the invention.

The device has numerous and various utilizations. It can be used fordegasing a liquid, treating a liquid containing solid particles insuspension, etc.

In addition, it offers advantages in the treatment of waters polluted bythe spillage of such a product as hydrocarbons. As a matter of fact,such a separation system makes it possible for example, to discharge awater substantially free of hydrocarbon traces.

FIG. 6 shows another possible use of the device according to theinvention.

As a matter of fact, let us consider a submerged oil well 32 producing adiphasic fluid, comprising liquid hydrocarbons and gaseous hydrocarbonsin such proportions that the pressure of this diphasic fluid cannot beincreased to the required value for its conveyance through line 33 bymeans of the presently available pumping equipment.

It is known that said diphasic fluid may be admixed with a sufficientamount of water to obtain a new diphasic fluid whose pressure may beincreased by the presently available pumping equipment. Preferably, thiswater is sea water, previously treated if necessary (by filtration etc.)and introduced into the diphasic fluid by means of a suitable mixer,diagrammatically shown in 34. Such a mixer is described, for example, inthe French patent application No. 2,417,057. After increase of thepressure by a pumping assembly 35, the water contained in the mixture iswithdrawn by means of the device 36 according to the invention in orderto be totally or partially discharged to the sea or optionallyreintroduced into the hydrocarbon diphasic mixture by the mixer 34.

Thus, only the liquid and gaseous hydrocarbons are introduced into thetransportation line 33 and no polluting discharge of hydrocarbons inwater is effected.

What is claimed is:
 1. A method of use of a device for separatingcomponents of a mixture of at least two immiscible fluids of differentspecific gravities, the device having inlet means connected to a tubularbody having at least one coaxial partition internally for withdrawingthe mixture at a first end of the tubular body and respective extractionmeans connected to the tubular body toward the second end thereof fordischarging the mixture, one of the at least two immiscible fluids andanother of the at least two immiscible fluids, first means for impartingto the mixture, when flowing through the body, a motion having arotational component about the axis of the tubular body, at least secondmeans adapted for imparting to the fluid passing therethrough arotational component about the axis of the tubular body and locateddownstream from the end of one of the partitions inside the tubularbody, and feedback means for feeding back the stream, issuing from thesecond end, to the inlet means, the method comprising: withdrawing adiphasic fluid comprising liquid hydrocarbons and gaseous hydrocarbonsfrom a submerged oil well; adding and mixing sufficient water to saiddiphasic fluid to form a second diphasic fluid capable of beingpressurized by a pump; pressurizing the second diphasic fluid with apump; separating the added water from the pressurized second diphasicfluid by passing it though said device for separating a mixture ofimmiscible fluids; and conveying the thus-pressurized diphasic fluid ofliquid and gaseous hydrocarbons through a pipeline.
 2. A method as inclaim 1 further comprising sensing the composition of the fluid beingdischarged through at least one of the respective extraction means andif the composition sensed consists essentially of only one of the fluidsof the mixture, discharging the one fluid sensed, and if the compositiondoes not consist essentially of only one of the fluids, recycling itagain to the inlet of the device for separating components to be furtherseparated.
 3. A method as in claim 2, wherein said sensing is conductedby measuring the electrical resistance of the fluidsbeing dischargedthrough at least one of the respective extraction means.
 4. A method asin claim 1, wherein the diphasic fluid further comprises solid particlesin suspension and the device further comprises a respective extractionmeans for said solids, said method comprising passing said diphasicfluid having solids in suspension through said device to therebyseparate said solids, and separate said fluids making up said diphasicfluids one from the other.
 5. A method as in claim 1, wherein said waterintroduced into said diphasic fluid is sea water introduced through amixer.
 6. A method as in claim 1 further comprising recycling theseparated water and mixing it with additional diphasic fluidhydrocarbons being withdrawn from the submerged well to conduct theprocess continuously.